In general, a submerged nozzle is widely used in continuous casting equipment, in order to introduce molten steel from a tundish into a mold. The submerged nozzle has a role of preventing re-oxidation of the molten steel due to direct contact with the atmosphere, and is an important refractory which makes a great contribution to improving the quality of the cast metal.
Furthermore, the flow of the molten steel discharged into the mold from the submerged nozzle affects the quality of the cast metal. For example, in rectangular molds, such as blooms, billets, or the like, it is important to supply as uniform a discharge flow as possible, at each of the mold surfaces, in order to prevent cracks in the cast metal. On the other hand, the surface quality of the cast metal is also improved by rotating and churning the molten steel inside the mold, since inclusions and air bubbles become less liable to be captured in the solidification shell.
A known method for churning the cast steel inside the mold, for example, is to provide an electromagnetic stirring device in the vicinity of the mold, and to use electromagnetic forces to churn the molten steel. However, since an electromagnetic stirring device is extremely expensive, there have been demands to carry out churning by an alternative, inexpensive system.
As a method for this, it has been attempted to create a rotational flow inside the mold by means of the discharge flow from a submerged nozzle, thereby churning the molten steel.
For example, Patent Document 1 proposes a method for obtaining a rotational flow by discharging a discharge flow in a tangential direction at a plurality of positions which are symmetrical with respect to the center of the discharge, and at an angle of 45±10° with respect to the square mold surface. Furthermore, it has also been proposed to form the discharge holes with a straight shape or curved shape.
Moreover, Patent Document 2 proposes a nozzle in which a portion of the inner wall of a discharge hole coincides with the tangent to the inner circumference of the nozzle.
Furthermore, Patent Document 3 proposes a method using a nozzle wherein the direction of discharge from a discharge hole is formed at an angle in the circumferential direction with respect to a radiating direction from the center, in such a manner that the submerged nozzle receives a reactive force produced when the molten steel is discharged, thereby causing the submerged nozzle itself to rotate about a perpendicular axis and hence causing the flow of molten steel flow to rotate.
Moreover, Patent Document 4 proposes a method wherein a discharge hole is arranged at an inclination to the radiating direction, the submerged nozzle is divided into two parts, an upper and a lower part, and the lower nozzle is caused to rotate about a perpendicular axis.
Patent Document 1: Japanese Patent Application Publication No. S58-77754
Patent Document 2: Japanese Patent Application Publication No. S58-112641
Patent Document 3: Japanese Patent Application Publication No. S62-270260
Patent Document 4: Japanese Patent Application Publication No. H10-113753